[R] regexp help needed

[Peter Dalgaard]

Lauri Nikkinen wrote:
> Hello,
> 
> I have a vector of dates and I would like to grep the year component
> from this vector (= all digits
> after the last punctuation character)
> 
> dates <- c("28.7.08","28.7.2008","28/7/08", "28/7/2008", "28/07/2008",
> "28-07-2008", "28-07-08")
> 
> the resulting vector should look like
> 
> "08" "2008" "08" "2008" "2008" "2008" "08"
> 
> I tried something like (Perl style) with no success
> 
> grep("[[:punct:]]?\\d", dates, value=T, perl=T)
> 
> Any ideas?

> sub(".*[[:punct:]]([0-9]*$)", "\\1", dates)
[1] "08"   "2008" "08"   "2008" "2008" "2008" "08"
> sub(".*[[:punct:]](.*)$", "\\1", dates)
[1] "08"   "2008" "08"   "2008" "2008" "2008" "08"
> sub(".*[[:punct:]]", "", dates)
[1] "08"   "2008" "08"   "2008" "2008" "2008" "08"
> substring(dates,regexpr("[0-9]*$", dates))
[1] "08"   "2008" "08"   "2008" "2008" "2008" "08"

(grep() won't do. It only tells you _whether_ the pattern matches.)


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